1. Field of the Invention
This invention relates to a laser inspection apparatus, for example, having an inspection function of detection, thickness measurement, etc., of an unremoved material left on the bottom face of a blind via hole during blind via hole machining in a multilayer wiring board called a printed wiring board.
2. Description of the Related Art
Making denser wiring has been demanded with recent high performance of the electronic machines. To meet the demand, multilayering and miniaturization of printed wiring boards are advanced. In one of the arts, it is indispensable to make a fine blind hole for interlayer conduction connection having a hole diameter of about 150 xcexcm, called a blind via hole (SVH). However, it is difficult to drill a hole of xcfx860.2 mm or less and machine a blind hole by the current drilling technique and in addition, an insulating layer of a high-density printed wiring board is 100 xcexcm or less thick and it is difficult to control the depth with the accuracy, thus it is impossible to make a fine BVH by drilling.
Attention is focused on a method of irradiating a laser beam as a BVH making method replacing the drilling. The method uses the light energy absorption difference between a resin or glass fiber of an insulating material forming a part of a printed wiring board and copper of a conductor layer. Carbon dioxide laser is put to some use as a light source of laser beam. As shown in FIG. 11, if inner layer copper foil 24 is previously deposited on the inside of the machined part, dissolving and removal of an insulating member are stopped on the inner layer copper foil 24, so that a blind hole 6 stopped reliably on the inner layer copper foil 24 can be made. Such a machined hole is particularly called a direct image hole. As shown in FIG. 12, on a board comprising copper foil 24a on a surface, a copper foil removal part of a necessary hole diameter is formed by etching, etc., and laser beam 20 having a beam diameter larger than the hole diameter of the removal part is applied, whereby a machined hole 6 can also be made. Such a machined hole is particularly called a conformal image hole.
If the blind hole stopped on the copper foil is machined by carbon dioxide laser as shown in FIGS. 11 and 12, the resin of the insulating member 1 xcexcm or less thick is left on the inner layer copper foil if a sufficient laser beam is applied. Thus, after laser machining, it is necessary to etch the residual resin in a permanganic acid, etc., for completely removing the residual resin. At this time, if the blind hole is lessened to about 100 xcexcin diameter, the etching liquid becomes hard to spread all over the inside of the hole, thus if the residual resin becomes thick exceeding a thickness of 1 xcexcm because of a failure of the laser machining condition, etc., a hole where the residual resin cannot completely be removed occurs. In this state, if plating is applied and a BVH electrode is formed, the resin remains left in a part between the plate film and the inner layer copper foil. Here, if a stress is exerted by a heat cycle, etc., with it as the start point, the plate film peels off. Thus, it becomes necessary to inspect the thickness of the remaining resin after laser machining.
FIG. 13 a residual resin distribution when the number of shots is changed. It is known that the residual resin is a little observed in the vicinity of the center of a hole and is easily left in the vicinity of the wall faces of the hole. Like a hole made with the number of shots, five pulses, the resin is a little observed at the center position, but is much in the surroundings as a defective piece. Therefore, to inspect the residual resin for thickness, it is necessary to inspect a wide range from the center to the periphery.
An inspection apparatus in a related art uses an optical microscope to inspect a machined part as shown in FIG. 14. If a resin is left about 10 xcexcm or more thick, it can be detected under the optical microscope in the related art described on page 45 of Nikkei Science October 1990 issue, but the optical microscope is poor in detection accuracy of the residual resin about several xcexcm thick as described above and is hard to apply in mass production. The post-plated machined part must be cut and ground, then the residual resin must be inspected for thickness by observing the cross section; the inspection takes time and 100% inspection cannot be conducted; this is a problem.
The reason why the residual resin cannot be detected under the optical microscope in the related art is as follows:
The optical microscope in the related art has a configuration as shown in FIG. 15. Illumination white light 38 is applied through an object lens 5 to a printed wiring board 21 by a beam splitter 25. Reflected light from the printed wiring board 21 forms an inverted real image 27 enlarged by the object lens 5 forward of an image formation lens 9, and the real image is detected by a CCD camera 11.
As shown in FIG. 16, when the while light 38 of illumination light of the optical microscope is applied to the surface of residual resin 22, some is reflected and other light passes through the residual resin 22 and reaches copper foil 24 on the bottom and is reflected thereon. Therefore, if the white light 38 is applied to thin resin on the copper foil as illumination light, most reflected light is returned from the copper foil 24 and thus the residual resin 22 becomes invisible.
FIG. 17 shows an inspection apparatus described as one embodiment in JP-A-7-83841. In the figure, numeral 43 denotes an ultraviolet laser light source, numeral 45 denotes a collimation lens, numeral 44 denotes a mirror, numeral 25 denotes a beam splitter, numeral 46 denotes a rotary polyhedral mirror, numeral 21 denotes a printed wiring board to be inspected, numeral 9 denotes an image reformation lens, numeral 48 denotes a pin hole, and numeral 47 denotes a photomultiplier (photomultiplier tube).
Next, the operation of the related art example is as follows: Laser beam generated by the ultraviolet laser beam source 43 is enlarged using the collimation lens 45. The enlarged laser beam is scanned using the rotary polyhedral mirror 46 and is condensed on the printed wiring board 21 through the object lens 5.
The ultraviolet light generated from the printed wiring board 21 by irradiating the laser beam reversely traces the incident path, is fed back recursively, and is guided into a recursive reflection sense system by the beam splitter 25 placed in the optical path. The ultraviolet reflected light is formed through the image formation lens 9. An image in the proximity of the application point of the laser beam to the printed wiring board to be inspected is observed on the image formation face. Only the center portion is separated through the pin hole 48 placed in the image formation face and is detected by the photomultiplier 47.
Since the inspection apparatus in the related art shown in FIGS. 15 and 16 is configured as described above, if the residual resin is thin, the reflected light is strong and the residual resin cannot be detected as described above; this is a problem.
The inspection apparatus shown in FIG. 17 executes laser scanning on the rotary polyhedral mirror. The laser beam scan line may shift from the center line of the blind hole because of a position shift at the blind hole machining time, worsening of precision of the scanner, etc. For example, if the residual resin is a little observed in the vicinity of the hole center at a good level, but the periphery is at a defective level like the blind hole made with the number of shots, five pulses, a good piece may be erroneously determined a defective piece because of a scan line shift; this is a problem.
To prevent this, it is necessary to make the scan line spacing sufficiently smaller than the hole diameter and scan the full hole bottom face, but it takes enormous time in inspection; this is a problem.
To inspect a conformal board, since copper foil exists on the board surface, if laser beam is applied to any other portion than a blind hole, fluorescence is not generated, thus a defective piece is erroneously determined a good piece; this is a problem.
It is therefore an object of the invention to provide an inspection apparatus capable of inspecting a recess reliably and at high speed.
According to one aspect of the invention, there is provided a laser inspection apparatus comprising a light source for outputting laser beam, application means for irradiating the laser beam from the light source to any desired position of a detected body, first detection means for detecting fluorescence generated from the detected body to which the laser beam is applied, and second detection means for detecting reflected light scattered on a surface of the detected body to which the laser beam is applied.
According to another aspect of the invention, there is provided a laser inspection apparatus comprising a light source for outputting laser beam, application means for irradiating the laser beam from the light source to any desired position on a board formed with a recess, detection means for detecting fluorescence generated from the board to which the laser beam is applied and outputting a detection signal, and control means for controlling the application means based on the detection signal, characterized in that the application means scans laser beam in a predetermined direction in the proximity of the recess, the detection means detects strength change of the fluorescence generated from the board as the laser beam is scanned, and outputs a detection signal, and the control means calculates a tentative center position of the recess on the scan line based on the detection signal, then the application means is controlled by the control means so as to scan laser beam in a direction passing through the calculated tentative center position and orthogonal to the scan line.
The control means discretizes the detection signal and sorts the discretized data in the level order of the detection signal and further makes a comparison with the diameter of the recess previously stored, thereby calculating the tentative center position of the recess.
According to still another aspect of the invention, there is provided a laser inspection apparatus comprising a light source for outputting laser light, application means for irradiating the laser beam from the light source to any desired position on a board formed with a recess, first detection means for detecting fluorescence generated from the board to which the laser beam is applied and outputting a first detection a signal, second detection means for detecting reflected light scattered on a surface of the board to which the laser beam is applied and outputting a second detection signal, and control means for controlling the application means based on the first and second detection signals, characterized in that the application means scans laser beam in a predetermined direction in the proximity of the recess, the first detection means detects strength change of the fluorescence generated from the board as the laser beam is scanned, and outputs a first detection signal, the second detection means detects strength change of the reflected light scattered on the board as the laser beam is scanned, and outputs a second detection signal, and the control means calculates a tentative center position of the recess on the scan line based on the first and second detection signals, then the application means is controlled by the control means so as to scan laser beam in a direction passing through the calculated tentative center position and orthogonal to the scan line.
The control means discretizes the first detection signal and sorts the discretizes data in the level order of the first detection signal and further makes a comparison with the diameter of the recess previously stored, thereby calculating the tentative center position of the recess.
The control means discretizes the second detection signal and sorts the discretizes data in the level order of the second detection signal and further makes a comparison with the diameter of the recess previously stored, thereby calculating the tentative center position of the recess.
The second detection means is placed so that the angle from the board face is set equal to or less than the aspect ratio of the recess.
The second detection means is placed like a ring.
The control means combines the first and second detection signals.
The control means discretizes a composite signal provided by combining the first and second detection signals and sorts the discretized data in the level order of the composite signal and further makes a comparison with the diameter of the recess previously stored, thereby calculating the tentative center position of the recess.
The application means executes scanning in the same direction two times or more.
The laser inspection apparatus further includes position detection means for detecting an actual scan position at the laser scanning time.